Photovoltaics can be made from a variety of different materials and by way of a variety of different processes. One of the more promising fabrication methods—from a cost standpoint at least—is to form continuous webs of photovoltaic material that are sequentially processed as the web moves along a production line. Thus, various layers of the photovoltaic devices are sequentially formed, one on top of another, as the web of built-up material progresses down the moving production line. Another fabrication method is to deposit the photovoltaic film on plate glass, which is the preferred method to fabricate CdTe solar cells.
In the past, electrical defects in the photovoltaic film have been studied by removing a sample from the production material and inspecting the sample offline. Removing a sample often introduces serious defects near the edges of the remaining photovoltaic material where the sample was removed.
Further, examining the sample offline means that the information cannot be readily used in an automatic feedback loop for control of the film deposition processes. Further, such offline testing is time consuming, which results in a potential greater loss of material, in the event of a process excursion.
What is needed, therefore, is a system that overcomes problems such as those generally described above, at least in part.